1. Field of the Invention
The present invention relates to an image bearing member, an image forming method and an image forming apparatus.
2. Discussion of the Background
Recently, organic image bearing members (organic photoconductor (OPC)) have been superseding inorganic image bearing members in the application to photocopiers, facsimile machines, laser printers and their multi-functional machines according to their good performance and various kinds of merits. Specific reasons are, for example, optical characteristics, for example, the width of the optical absorption wavelength range and the amount of optical absorption, electric characteristics, for example, the high sensitivity and the stable charging characteristics, the wide range of selection for materials, easy manufacturing, low cost, and non-toxicity.
On the other hand, the diameter of an image bearing member has been recently reduced according as the size of an image forming apparatus is reduced. On top of that, high-speed performance and maintenance-free have been required. Therefore, an image bearing member having a high durability is demanded. An organic image bearing member includes a photosensitive layer mainly formed of a low molecular weight charge transport material and an inactive polymer. Such an image bearing member is soft in general. This leads to a problem that, while an organic image bearing member is repeatedly used in the electrophotographic process, abrasion thereof tends to occur due to the mechanical burden on the organic image bearing member received from a developing system and a cleaning system. In addition, toner particles have been reduced to obtain quality images, which requires improvement on the cleaning property and leads to increase in the hardness of the rubber for use in a cleaning blade and the contact pressure thereof to an image bearing member. This is one of the causes which accelerate the abrasion of an image bearing member. Such abrasion of an image bearing member degrades electric characteristics thereof, for example, sensitivity and chargeability. Thereby, image density deteriorates and the background fouling occurs, resulting in abnormal images. In addition, scars locally made on an image bearing member due to the abrasion invite poor cleaning performance, which leads to fouling in a streak manner on an image. In the current status, abrasion and scars on an image bearing member determines the timing of exchange thereof.
Therefore, it is inevitable to decrease the amount of the abrasion to improve the durability of an organic image bearing member. Furthermore, to impart an excellent cleaning property and transferability, an organic image bearing member having a good surface property is desired. This is an imminent issue to be solved in this area.
As a method of improving an anti-abrasion property of a photosensitive layer, published unexamined Japanese patent application No. (hereinafter referred to as JOP) S56-48637 describes a surface layer containing a curing binder. JOP S64-1728 describes a surface layer in which a polymer type charge transport material is used. JOP H04-281461 describes a surface layer in which an inorganic filler is dispersed.
In the method described in JOP S56-48637, due to an insufficient compatibility with the charge transport material and the presence of impurities, for example, polymerization initiator and unreacted remaining groups, the remaining voltage tends to rise and the image density tends to deteriorate.
In addition, the methods described in JOPs S64-1728 and H04-281461 possibly improve the anti-abrasion property of an organic image bearing member but do not improve the anti-abrasion property to a level desired therefor.
Furthermore, in the method described in JOP H04-281461, the remaining voltage easily rises due to the trapped charge present on the surface of an inorganic filler, which leads to the tendency of the deterioration of the image density.
These methods do not sufficiently provide an organic image bearing member with the total durability desired therefor including electric durability and mechanical durability.
Furthermore, Japanese patent No. (hereinafter referred to as JP) 3262488 describes an image bearing member containing a polyfunctional curing type acrylate monomer to improve the anti-abrasion property and anti-damage property described in JOP S56-48637. In this image bearing member, the protective layer, which is provided on the photosensitive layer, contains a polyfunctional curing type acrylate monomer. However, only there is a description that the protective layer can contain a charge transport material. Furthermore, when a surface layer simply contains a charge transport material having a low molecular weight, a problem of the compatibility with the cured material arises, which causes problems such that the charge transport material having a low molecular weight precipitates, cracking occurs and the mechanical strength deteriorates. In addition, to improve the compatibility, it is also described that a polycarbonate resin is added to the surface layer but as a result, the content of the cured material decreases and a sufficient anti-abrasion property is not obtained. Furthermore, with regard to the image bearing member in which the surface layer does not contain a charge transport material, there is a description that the surface layer is made to be thin to address the decrease in the voltage on the irradiated portion. However, because the image bearing member has a thin surface layer, the life thereof is short. Furthermore, since the environmental stability of such an image bearing member is low, the charged voltage and the voltage at irradiated portions significantly vary depending on the temperature and humidity. Therefore, it is difficult to maintain a sufficient value.
As an anti-abrasion technology for a photosensitive layer replacing these, JP 3194392 describes a method in which a charge transport layer is formed by a liquid of application containing a monomer having a double linkage of C—C, a charge transport material having a double linkage of C—C, and a binder resin. This image bearing member has a good combination of anti-abrasion property and electric characteristics and draws attention. However, when a non-reactive binder resin is used, the binder resin and a cured material formed through the reaction between the monomer and the charge transport material are not sufficiently compatible, causing phase reparation. This tends to lead to the formation of a convexo-concave surface during cross-linking and result in a bad cleaning performance. Additionally, the binder resin prevents the curing of the monomer. The specifically described monomers are di-functional so that the obtained cross linking density is not sufficient and the anti-abrasion property is not satisfactory. Furthermore, even when a reactive binder resin is used, since the monomer and the binder resin have a low number of functional groups, it is difficult to have a good combination of the content of linked charge transport materials and the cross-linking density and obtain sufficient electric characteristics and anti-abrasion properties.
JOP 2004-66425 describes a photosensitive layer containing a compound cured from a positive hole carrier transport compound having at least two chain-reaction polymeric functional groups in one molecular. However, since this photosensitive layer contains bulky positive hole carrier transport compounds having at least two chain reaction polymeric functional groups, distortion may occur in the cured material, which invites a high internal stress and leads to the roughness of the surface layer and the occurrence of cracking over time. Resultantly, the photosensitive layer does not have a sufficient durability.
Furthermore, JOPs 2004-302450, 2004-302451 and 2004-302452 describe a cross linking charge transport layer cured from a radical polymeric monomer having at least three functional groups which does not have a charge transport structure and a radical polymeric monomer having one functional group which has a charge transport structure. The radical polymeric monomer having one functional group which has a charge transport structure imparts electric and mechanical durability and also restrains the occurrence of cracking in the photosensitive layer. However, a monomer having a relatively large number of acrylic groups is used to improve anti-abrasion property when this cross linking charge transport layer is formed. Thereby, the volume contraction ascribable to a cured acryl compound is significant, which may cause insufficient adhesion between the cross linking charge transport layer and a photosensitive layer, which is provided therebelow. As a result, when such an image bearing member is used in an image forming apparatus having a large mechanical hazard to an image bearing member, a problem arises that the cross linking charge transport layer detaches and a sufficient anti-abrasion property is not maintained for an extended period of time.
JOP H02-5069 describes a method in which the durability of an organic image bearing member having a low mechanical strength is improved and the detachment of a surface layer is prevented by providing an intermediate layer formed of a metal dispersion layer having a low resistance on the organic image bearing member and an amorphous carbon hydride layer having a high mechanical strength on the intermediate layer as a surface layer by a plasma polymerization method. However, this method is to achieve the object of preventing deterioration of the surface of an organic image bearing member caused by exposure thereof to a plasma having a high energy. Furthermore, metal particulates dispersed in the intermediate layer is low resistant so that charges can be flow in the latitude direction, which inhibits the formation of an appropriate image.
JPs 2932679 and 2990788 describe a technology of providing an inorganic thin film protective layer on a rough surfaced photosensitive layer. The protective layer provided on the image bearing member described in JOP 2932679 is an inorganic thin film and therefore does not have a sufficient effect on the organic cross linking type protective layer of the present invention. In addition, the object of the improvement described in JP2990788 is to prevent the occurrence of image noise, film deficiency, toner filming, etc., which is totally different from the object and the effect of the image bearing member of the present invention.